The natural medium of the soil is the self-regulating ecosystem of the plants and micro-organisms, under natural circumstances, the existence of the former determines that of the other ones. When the balance developed in the course of the evolution is altered by human activities (deep ploughing, natural and artificial fertilisation, use of plant-protecting agents, etc.) in its structure and function, changes of non foreseeable effect can occur. For the development of the micro-organism populations needed for the optimal cultivation of a given cultivated plant, on the different soils and under different climatic circumstances, a selection time lasting for long years is needed. The determinant micro-organisms of the favourable micro-organism population, however, can be transported in the soil and the circumstances needed for the optimal cultivation can be created within one-two days. The result of this is the higher yield, without the harmful upsetting of the natural ecosystem. The useful and dominant micro-organisms existing in the environment of a given plant important from economic point of view can be determined by laboratory experiments and these can be individually multiplied, produced by industrial methods, and can be brought back in the soil in proper proportion.
Important regularities can be discovered in the ecosystem of the soil and micro-organisms. The number of the micro-organisms is different and different species can be identified in the immediate environment of the root system of the living plants (rhysosphere) and the germinating seeds (spermatosphere) than more remote from these. The propagation of the bacteria in the environment of the root is influenced by many factors. These factors depend on the region, quality of the soil, composition of the micro-organism population, and on the climatic circumstances.
The carbon source to be found in the soil comes into being primarily and in the overwhelming majority by using the solar energy, with photosynthesis.
The nitrogen cycle is more complicated than that of the carbon. On the transformation of nitrogen, biological and chemical processes have an effect. In the nature, the gaseous nitrogen in a so-called inert condition is dominant, and the so-called fixed nitrogen (nitrate, nitrite, ammonia) is present in a limited quantity.
For the mineralization of the nitrogen gas first of all the biological nitrogen binding is responsible. Since over one hectare the quantity of the molecular nitrogen amounts to 6-7×108 tons, this means an inexhaustible source for the nitrogen bound. The interest of the experts is directed towards the nitrogen binding living beings, i.e. towards the living beings, which can reduce the molecular nitrogen to ammonia since, among others, the knowledge of these micro-organisms and the adequate utilisation of their properties can ensure, in an environment friendly manner, the world-wide ceasing of the hunger.
Some nitrogen binding bacteria fix the nitrogen in free living condition but numerous bacteria are capable of nitrogen fixing only combined with other, higher plants.
The phosphorousous cycle, contrary to that of the nitrogen, is practically closed under natural circumstances. The input and output are identical, the flow is slight, the air won't be contaminated with phosphorousous. Finally, this element accumulates in the waters, seas, and only a slight quantity of this gets back to the land (for instance in the form of guano).
In the living cells of the soil the phosphorousous accumulates in organic compounds, the mineralization of these takes place with a high speed (3-8 g/m2/year). The solubility—so their accessibility for the plants—of the arising phosphorousous compounds is different, merely 5% of the 400-1200 mg phosphorousous detectable in each 1 kg of the average soils is available. The turnover of certain phosphorousous compounds is 500-2000 years.
By transporting some phosphonolytic micro-organism groups in the soil, the complex phosphorousous compounds, which are not accessible for the plant, can be brought in solution. If the micro-organisms brought in the soil “function”, and the mineral contents of the soil are satisfactory, the use of the fertilizers containing phosphate is not necessary or can be considerably reduced.
For growth, the plants need—especially at the time of the ripening of the crop—potassium of a considerable quantity. The plant cultivators bring the potassium in the soil by feeding of fertilizer with potassium content. This fertiliser can be made available from the potassium minerals by means of the micro-organisms releasing the potassium ion.
As far as the plants are concerned, the micro-organisms multiplying in the soil biosynthetize physiologically active compounds, out of these the most important compounds being: phytohormones, auxins (indole-3-acetic acid), ethylene, gibberellines, kinetins, etc. Some Pseudomonas groups, in the presence of iron of a slight quantity, produce so-called siderophores, which can collect the iron. As a consequence of this, the other, phytopathogenic bacteria and fungi, since these cannot utilize the iron from the siderophores, suffer inhibition owing to the lack of iron, on the other hand, these siderophores, in soil with lack of iron, significantly stimulate the growth of the plants, since binding the iron, these directly provide the iron for the plant.
For the solution of the above, several technical versions had been elaborated; several micro-organisms are described in the special literature in full details.
Hungarian inventors disclosed the preparation of powdered nitrification cultures (Hungarian patent HU 143.391), Azobacter chroococcum and Rhizobium meliloti cultures (Hungarian patent HU 188.434), alga cultures (Hungarian patent HU 195.068) and Azotobacter chroococcum cultures again, as well as the preparation of the cultures of Bacillus megaterium micro-organisms (Hungarian patent HU 207.751). The Azobacter chroococcum had been deposited under the deposit No. 00238, the Bacillus megaterium under the serial No. NCAIM /P/ B 1140. More detailed, in Hungarian patents HU 188.434 and HU 207.751, the authors describe the fermentation turning out of the mixture of the above deposited micro-organisms. According to Hungarian patent HU 213 163 the authors complete the culture of the microorganisms of HU 207.751 with carboxy-methyl-cellulose. Hungarian inventors in HU 1671/96 describe cultures containing Azospirillum lipoferum ssp., Azobacter vinelandi sp., Pseudomonas fluorescens ssp. and Bacillus megaterium ssp. micro-organisms.
The application and effect of the micro-organisms applied in the mentioned procedures are limited by the fact that these, under different cultivation circumstances, in soils of various compositions, under different climatic circumstances, survive only for a short time, the environment and rhysosphere of the various plants not always create optimal conditions.